Solar cells, or photovoltaic cells, are one of the key technologies being used in the development of sustainable energy. These cells have been used to power space probes, satellites, and to provide electricity in remote areas where other energy sources are not available. Solar cells have also been used in small consumer products, such as calculators, for several years. More recently, hybrid power supplies have been constructed using large-panel solar modules connected to an electrical grid. Most consumers have several low cost options for supplying their electricity needs. Therefore, the ultimate success of any photovoltaic cell will depend upon its ability to efficiently produce electricity at a low cost.
Photovoltaic cells operate by using semiconductors to convert photons from the sun into electricity. More specifically, electricity is produced when photon energy is absorbed in the active region of the photovoltaic cell, and the absorbed energy generates electron-hole pairs. The amount of energy required to generate the electron-hole pairs is known as the band gap energy, and is generally equal to the minimum energy required to excite an electron from the valence band to the conduction band.
In order to recover electrical current when exposed to solar radiation, photovoltaic cells must have electrical contacts, or electrodes, on both their front and rear sides. The contact on the front side of the cell is usually shaped as a grid comprising a plurality of narrow, elongated parallel fingers, and at least one elongated busbar that intersects the fingers at a right angle. Rear contacts may also be configured using a grid design, but more often are made of a fully metal layer. Typically, the area of the solar cell surface covered by the grid is minimized to reduce the reflection of sunlight off the metal grid. On the other hand, it is also desirable for the grid to be as densely populated as possible in order to minimize the overall resistance of the contact structure.